Microfluidic test cartridge s for use in test instruments are used to process samples, such as blood samples and transport the processed samples to areas on the cartridge for the performance of one or more tests. The amount of sample, such as in the case of blood may be limited. Movement of the sample through the cartridge during processing can be difficult to track and stop at an appropriate time.
To determine the percent activation energy of an individual's platelet sample, the images of a single plasma sample, in two different conditions is taken and analyzed. One plasma condition includes untreated platelet rich plasma (PRP) condition of a blood sample taken from a patient (baseline state), while a second plasma condition is observed after exposure (and shear) to an agonist. In order to image the platelets clearly, everything in imaging windows of the microfluidic cartridge should be stable (both plasma and platelets in the plasma). In previous methods, a sample would have to be manually stopped by turning off the pump. The sample would continue to flow past the stopping point while, wasting time waiting for equilibrium to be reached in the microfluidic cartridge. The lesser results were that the shear rate was not known and the time to stop the sample varied, but more often the sample would be pushed completely out the microfluidic cartridge.
Other prior devices include an LTA (light transmission agregometer), using two physically different platelet samples from a patient. The light transmission of the untreated sample would be measured and then the agonist would be added to the 2nd sample, the sample sheared and, while shearing, the transmitted light would be measured through the sample tube. As the platelets aggregated, the amount of light transmitted through the tube would decrease, but as they reached a critical size and dropped down to the bottom of the tube, more light would be transmitted through the tube. The test would typically take about 10 minutes.
Other methods include using electronic measurements to measure the conductivity across a platelet sample. Two platelet samples were required, such as the Mindray (Helena) method. The problem with these methods is that hand shear is done by shaking the sample tube, repeatably from sample to sample which is extremely difficult to do.